In relation to oxide-based solid electrolytes for use in all-solid batteries, it is known that crystals (perovskite type and garnet type), glass ceramics and the like are high in ion conductivity. However, both in the crystals and in the glass ceramics, in order to realize a high ion conductivity, it is necessary to sinter the solid electrolyte at a high temperature of not less than 700° C.
In the case of using a solid electrolyte for battery electrodes, in general, it is necessary to fire a composite body containing an electrode active material and the solid electrolyte, thereby sintering the solid electrolyte. If the sintering temperature is high as aforementioned, however, the electrode active material and oxygen in the solid electrolyte or air might react with each other in the firing step of the composite body. For restraining such a reaction, it is desirable to set the sintering temperature at or below 600° C.
As a technology for obtaining a high lithium ion conductivity upon low-temperature sintering, the followings have been proposed, for example.
In PTL 1, it is proposed to mix and mold a garnet type compound and a phosphoric acid group-containing lithium conductor, thereby enhancing ion conductivity without performing high-temperature sintering.
In PTL 2, it is proposed to sinter a mixture containing an LAGP glass ceramic and amorphous Li—Al—Si—O, thereby obtaining a solid electrolyte sintered body that has an ion conductivity of 5×10−5.
In PTL 3, it is proposed to sinter a raw material body containing a garnet type compound and Li3BO3, thereby obtaining a solid electrolyte that has an ion conductivity of approximately 4×10−6.